The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Control modules on-board a land vehicle can control vehicle operation, including, e.g., engine, transmission, power management, chassis, braking, steering, and other systems. Furthermore there can be a plurality of information and entertainment (infotainment) services available, including, e.g., AM/FM radio, portable music players, cellular phones, GPS navigation, satellite radio, remote keyless entry, and remote vehicle starting. Control modules are preferably spatially located near the functional area they control to minimize length of wiring harnesses to sensing devices and actuators. Thus, an engine control module is preferably placed in or near an engine compartment and infotainment modules are placed in a passenger compartment. However, vehicle space utilization is becoming more problematic as features are added to an already limited packaging environment. Wire harness routing and availability also may limit the positioning of control modules into certain locations of the vehicle that may otherwise be acceptable.
A control module may need to communicate with one or more of the other control modules in a vehicle. Known communication methods include a wired local area network that has a shared communications bus. Wireless communication is also possible. In addition, portable wireless devices and other applications can be interfaced with an on-vehicle control module and the vehicle's user interface devices. For example, cellular phones equipped with a wireless communications system can utilize the vehicle speakers and a microphone to enable hands-free calling. A portable music player device can use an embedded audio/visual system to play back music and other audio and/or video files.
Wireless communications protocols for communicating between control module devices include IEEE 802.15.1 and IEEE 802.11 wireless protocols. The IEEE 802.15.1 wireless communications protocol uses a secure, unlicensed ISM 2.4 GHz short-range radio frequency bandwidth. Use of the IEEE 802.15.1 wireless communications protocol facilitates short range (1 to 10 m), low power wireless communications using a low-cost transceiver. The IEEE 802.11 wireless communications protocol also uses a secure, unlicensed ISM 2.4 GHz radio frequency bandwidth with a longer range (32 to 95 m) and increased power consumption.
Wireless communications require the use of an antenna connected to a transceiver device. Thus, each control module using wireless communications requires an antenna connected to a local transceiver device. Antenna design is critical to achieve effective range and signal throughput. Antenna design criteria include antenna shape, size, and length that are tuned to a communications wavelength and to the effects of the neighboring environment including metallic and dielectric materials including ground planes. Antenna performance and operating characteristics include gain, radiation pattern, polarization, radiation resistance and input impedance.
One method to design an antenna is to create an electrical resonate structure. When electrically excited at the resonant frequency, the resonate structure ‘leaks’ energy that radiates away from the structure. For example, a half-wave length resonate structure is created with an antenna length that is approximately a half-wavelength, which is half the wavelength of the intended radio frequency (RF) field.
Different antenna structures have been proposed for on-board short range wireless communications, including external antennas and antennas formed by depositing conductive films, strips, dielectric materials or wires on printed circuit boards. In order to make an antenna fit into allowable packaging space, one or more of the antenna performance characteristics may be impaired.